The present invention relates to a method of measuring a three-dimensional position of a workpiece, which can be suitably applied to a case in which white balance and cut-off of an industrial display unit (hereinbelow, referred to as a "display unit") are automatically adjusted by a robot.
Conventionally, it is difficult to position a display unit with high precision during production processes of the display unit due to rotational construction of the display unit or peculiar shape of its cathode ray tube. Therefore, it is also difficult to position a printed circuit board attached to a rear portion of the cathode ray tube and thus, the printed circuit board is positioned manually in many cases.
In order to automatically adjust white balance and cut-off of the display unit, such methods have been tried that (1) the printed circuit board attached to the rear portion of the cathode ray tube is secured by a jig and (2) reading of a present position of the printed circuit board by bringing a probe into contact with the printed circuit board by a robot enabling force control is repeated at a total of 6 points such that a three-dimensional position of the printed circuit board is obtained.
However, in the method (1), since many models of the display units are proposed in recent years, position of the jig should be changed according to the models of the display units. Furthermore, in the case of a display unit having rotational construction, the method (1) has such a drawback that it is next to impossible to fix position of the jig.
Meanwhile, in the method (2), since accuracy of force control of the robot is poor and the printed circuit board is deflected through its contact with the probe, it is difficult to obtain accurate position of the printed circuit board. In addition, the method (2) has such a disadvantage that since measurement is performed at 6 points, a measuring period is increased.